Photoprocessing stabilizer solutions

ABSTRACT

AN IMPROVED STABILIZER COMPOSITION FOR USE IN THE RAPID PROCESSING OF A LIGHT SENSITIVE SILVER HALIDE EMULSION IS DISCLOSED. A TYPICAL COMPOSITION COMPRISES 150-350 GRAMS AMMONIUM THIOCYANATE, 0.1-1.0 GRAMS 1-PHENYL1,2-TETRAZOLINE-5-THIONE, AND 25-150 GRAMS MONOBASIC POTASSIUM PHOSPHATE AND WATER TO ONE LITER OF SOLUTION THESE COMPOSITIONS ARE PARTICULARLY USE FOR THE RAPID PROCESSING OF PHOTOGRAPHIC ELEMENTS WHEREIN THE SILVER HALIDE EMULSION LAYER CONTAINS DEVELOPING AGENTS THEREIN OR CONTIGUOUS THERETO AS A SEPARATE LAYER. PRINTS PROCESSED WITH THESE COMPOSITIONS HAVE BEEN FOUND TO BE HIGHLY RESISTANT TO DISCOLORATION, FADING AND STAINING ON BOTH THE EMULSION AND BASE SIDES OF THE PRINT.

United States Patent 3,829,318 PHOTOPROCESSING STABILIZER SOLUTIONS Irving J. Magin, Henrietta, N.Y., assignor to Itek Corporation, Lexington, Mass.

No Drawing. Filed Sept. 25, 1972, Ser. No. 291,873 Int. Cl. G03c 1/06, 5/38 US. CI. 96-61 R 11 Claims ABSTRACT OF THE DISCLOSURE An improved stabilizer composition for use in the rapid processing of a light sensitive silver halide emulsion is disclosed. A typical composition comprises 150-350 grams ammonium thiocyanate, 0.1-1.0 grams l-phenyl- 1,2-tetrazoline-5-thione, and 25-150 grams monobasic potassium phosphate and water to one liter of solution. These compositions are particularly useful for the rapid processing of photographic elements wherein the silver halide emulsion layer contains developing agents therein or contiguous thereto as a separate layer. Prints processed with these compositions have been found to be highly resistant to discoloration, fading and staining on both the emulsion and base sides of the print.

BACKGROUND OF THE INVENTION (1) Field of the Invention This invention relates to stabilizer solutions useful for photoprocessing and more particularly to improved aqueous, acidic stabilizer solutions for the rapid processing of photosensitive silver halide emulsions.

(2) Description of the Prior Art For many applications, particularly in automatic processing machines, such as microfilm reader-printers, it is advantageous to be able to rapidly process an exposed photosensitive silver halide emulsion. Rapid processing methods are known in the art, and such methods have been described in such patents as: Brice, US. 2,448,857; Broughton et al., US. 2,614,927; Smith et al.; U.S. 3,132; 943 and 3,137,574.

Generally, these rapid processing methods are accomplished by contacting the exposed photosensitive emulsion with a typical developer composition, or an alkaline activator solution for developing agents in or contiguous to the emulsion, followed by immersion of the emulsion in a stabilizer solution. After stabilization, the print can be dried without performing the conventionally required fixing and washing steps, thereby saving time.

Prior art stabilizer solutions have traditionally been acidic, aqueous solutions containing high concentrations of a stabilizing agent. Common stabilizing agents are compounds containing a double-bonded sulfur or an SH linkage such as alkali metal thiocyanates. One of the most commonly used stabilizing agents is ammonium thiocyanate. Various acids, suchas acetic, propionic, butyric, mucic, citric and tartaric, etc., have been proposed to obtain the desired pH which is well into the acid range.

While the above-described method of stabilizing the prints makes rapid processing possible, it has been recognized by the art that it is accompanied by many defects in the developed photographic prints. For example, since the stabilizing agent is typically used in high concentrations and in amounts considerably greater than the theoretical amount necessary to secure the light stability of the developed print, excess stabilizing agent remains on the surface of the print following processing. This causes gradual oxidation of metallic silver in the developed image with the formation of a silver complex salt which reduces image density or causes fading. In addition, formation of the silver complex salt results in a 3,829,318 Patented Aug. 13, 1974 change of colortone from black to brown or yellow due to depletion of the metallic silver. Also, with certain prior art stabilizing composition, brown or yellow staining of the emulsion and/ or base sides of the developed photographic print occurs with aging. These problems are particularly aggravated under conditions of elevated temperature and high humidity.

Another problem noted with prior art stabilizer compositions is their limited life. With repeated use, prints of poor image quality are obtained due to carryover of the alkaline developing agent into the stabilizing composition which results in an increase of the stabilizer pH beyond that level at which the stabilizer is effective. This is a particularly serious problem in automatic processing machines.

SUMMARY OF THE INVENTION It has now been found that an exposed and developed silver halide emulsion can be stabilized to be highly resistant to discoloration, image fading and/or staining by contacting the emulsion with an acidic, aqueous stabilizer composition, comprising, per liter of solution: (1) -350 grams of a water-soluble stabilizing agent, preferably an alkali metal or ammonium thiocyanate; (2) 0.1-1.0 grams of l-phenyl-1,2-tetrazo1ine-5-thione; and, (3) a buffering agent, such as potassium dihydrogen phosphate, present in sufficient quantities to provide a pH between 2.75 and 5 and to provide substantial buffering I during processing of the emulsion.

The rapid photoprocessing of a silver halide emulsion in accordance with this invention includes the steps of exposing the photographic element having a light sensitive silver halide emulsion thereon, developing by contact with the developing solution or an activator solution, and stabilization by cont-act with the above-noted stabilizer composition. After the development step, it is desirable to remove excess developing solution present on the surface of the print by convenient means such as a squeegee. After stabilization, the print can be dried directly.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The light sensitive silver halide emulsions useful for the formation of photographic elements processed with the stabilizer compositions of this invention include any of the known silver halide developing-out emulsions such as silver chloride, -chlorobromide, -chloroiodide, -chloro bromoiodide, -bromide, or -bromoiodide developing-out emulsions. Any of the known permeable hydrophilic colloids can be used for the silver halide emulsions. Typical water permeable hydrophilic colloids include gelatin, albumin, polyvinyl alcohol, agar agar, sodium alginate, hydrolyzed cellulose esters, hydrophilic polyvinyl c0- polymers, etc. In a preferred embodiment of the invention, the photographic elements also contain developing agents for the silver halide emulsion, either dispersed in the emulsion layer itself or in layers contiguous thereto coated on the emulsion layer as a separate layer dispersed in another water-permeable hydrophilic colloid layer, or both.

Useful developing compositions and activator compositions are also well known. Typical are polyhydroxy benzenes such as the hydroquinone, and substituted hydroquinone. Substituted hydroquinones include alkyl-substituted hydroquinones, aryl-substituted hydroquinones and other hydrocarbon-substituted hydroquinones, carboxyl-substituted hydroquinones, acyl-substituted hydroquinones, acyloxy-substitu-ted hydroquinones, alkoxysubstituted hydroquinones, halo-substituted hydroquinones, etc.

Photographic elements and typical developing agents as mentioned above are described in more detail in the patents referred to above and in the following additional patents, the" teachings of which are incorporated by reference: Kennard et al., U.S. 3,192,046; Porter et al., U.S. 3,246,988; Ryan et al., U.S. 3,262,781; and, Porter et al., U.SL 3,291,609.

To rapidly process photographic elements in accordance with the process of this invention, they are exposed to a suitable original or record and contacted with a developer or activator for a short period of time, usually less than ten seconds. Where the developing agent is dispersed in the emulsion or in a layer contiguous thereto, the activator may be an alkaline solution such as a solution of sodium carbonate, sodium hydroxide, potassium carbonate, potassium hydroxide or mixtures thereof. Where the silver halide emulsion is not combined with the developing agent, the silver halide emulsion is developed by immersion in a conventional developer such as those enumerated above and known to the art.

Following development of the silver halide emulsion, excess developer or activator solutions is removed from the surface of the photographic element by conventional means such as a squeegee. The developed emulsion is then immersed in a stabilizer composition for a short period of time preferably, less than five seconds. The stabilizer compositions of this invention contain certain specified amounts of a stabilizing agent, l-phenyl-1,2-tetrazoline- -thione and a buffering agent.

Suitable stabilizing agents for this invention are those water soluble compounds which, when dissolved in acidic solutions, stop or substantially inhibit further development of the silver image and tie up undeveloped silver ions. Usually, these are compounds which contain doublebonded sulfur or an SH linkage; for example, alkali metal or ammonium thiocyanates, thiosulfates, thioureas, or thioglycolic acids. Alkali metal or ammonium thiocyanates are preferred because of their excellent stabilizing properties. The stabilizing agent is used in an amount of between about 150 and 350 grams per liter of stabilizing solution. This amount is lower than that used in many of the known stabilizer solutions, particularly when the solution is used in an automatic processor which operates at higher than normal speeds, i.e., one which processes 350 square feet or more of silver halide paper per liter of stabilizer solution at a speed of feet per minute.

Additionally, the stabilizer compositions of this invention contain from about 0.1 to 1.0 grams per liter of solution of a l-penyl-1,2-tetrazoline-5-thione having the following formula or a tautomeric equivalent thereof:

The phenyl group may be substituted, as for example where R in the above structural formula is selected from lower alkyls, lower alkoxy, amino or a halogen. These compounds have been found to be particularly efficacious in the reduction or elimination of staining of the silver halide emulsion or base.

As is known, stabilizer compositions are required to be in the acidic pH range to stop the action of the alkaline developer solutions. The compositions of this invention include an acidic buffering agent in suflicient amounts to provide the solution with an original pH of between about 2.75 and 5, and also to provide substantial buffering to the stabilizer solution during processing of the silver halide emulsion. Some buifering agents which are suitable and known to the art include acetic acid, phosphoric acid and certain of its salts, certain metabisulfites such as alkali metal or ammonium metabisulfites, and some of the other agent is r'rionobasic potassium phosphate (KH PO which has been found to have superior buffering characteristics even over other phosphoric acid salts. For example, it has been found that up to 660 square feet of silver stabilization paper can be processed with one batch (1.7 liters) of stabilizer solution before the pH rises to an unacceptable levelJMonobasic potassium. phosphate has the additional advantages of: (1) not having the objectionable odor of some buffers, such as acetic acid; and (2) not producing volatile gases which are toxic or cause the containers to bulge or split the plastic container under certain environmental conditions, such as some of the metabisulfites.

In a more preferred embodiment, the stabilizer compositions of this invention contain about 280:10 grams of a stabiilzing agent, 0510.2 grams of 1-phenyl-l,2-tetrazoline-S-thione, per liter of solution, and a buffering agent sufficient to lower the pH to an original value below about 3.5 and to provide substantial buffering action during processing of the emulsion; The most preferred composition, because of its excellent stabilizing characteristics, its long life, and its reduction or elimination of staining, image fading or discoloration is:

Grams Ammonium thiocyanate 280:10 l-phenyl-l,2-tetrazoline-5-thione 05:0.2 Potassium dihydrogen phosphate 50:10

Water to one liter.

The invention is further illustrated by the following examples. All parts and percentages are by weight unless otherwise specified.

EXAMPLE 1 Grams Sodium hydroxide 50 Sodium sulfite 50 Sodium thiosulfate 4 Potassium bromide 2 Water to 1 liter.

Stabilizer solution was applied from a dip tray and subsequently squeegeed off after stabilization. The stabilizer solution had the following formula:

' Grams Ammonium thiocyanate 280 Monobasic potassium phosphate "50 l-phenyl-1,2-tetrazoline-5-thione 0.5

Water to 1 liter.

The pH of the stabilizer solution was measured after different amounts of paper had been processed. The results were:

Stabilizer pH:

From the above, it can be seen that the stabilizer solution is capable of processing large amounts of silver halide stabilization paper before its pH rises to a level making it inefficient for further processing.

EXAMPLE 2 The processing conditions and equipment of Example 1 were used except that 'a new Stabilizer solution was used which had thefollowing formula:

. Grams Ammonium thiocyanate 280 D ib asiic sodium phosphate -l 50 l-phenyl-1,2-tetrazoline6-thione 0.5

Water to l liter.

Stabilizer pH: Paper processed (it?) EXAMPLE 3 The processing conditions and equipment were the same as in Example 1 except that a different stabilizer solution was used which had the following formula:

Grams Ammonium thiocyanate grams 280 Sodium sulfite dn 5 Sodium metabisulfite do 32 1-phenyl-5-mercaptotetrazole do 5 Ethyl alcohol milliliters 200 Water to 1 liter.

This stabilizer solution is taught at col. 2, lines 3743 of U.S. 3,404,981.

Measurements of the pH at different processing points produced the following results:

Stabilizer pH: Paper processed (ft?) 0 EXAMPLE 4 Stabilizer 01- Example Example Example 1 2 3 Original density 0. 60 0. 54 0. 54 Density loss 0. 09 0. 16 0. 14

Original density 0. 20 0. 19 0. 17 Density loss 0. 06 0. 12 0. 11

As can be seen from the above results, the density loss after 14 days is significantly reduced using a stabilizer having the formula of Example 1, contrasted to the other stabilizer solutions used.

6 EXAMPLE 5 Titrations were run on two different stabilizer solutions, one having the formula of Example 1 and the second having the formula of Example 3. Fifty, milliliters of each of these formulations were placed into a flask and titrated with 5 sodium hydroxide solution. The following results were obtained: 1 Example 1 stabilizer solution:

M1. 5% NaOH Example 2 stabilizer solution:

P Ml. 5% NaOH 5.50 2.8 6.00 8.7 6.50 17.7

These titrations demonstrate that the stabilizer solution having a formula of Example 1 is able to accept more activator carryover before the pH reaches an inefficient level.

What is claimed is:

1. An aqueous photoprocessing stabilizer solution, comprising, per liter of solution:

(a) from about to about 350 grams of a watersoluble stabilizing agent selected from an alkali metal or ammonium thiocyanate, thiosulfate, thiourea, thioglycol in acid, or combinations of these;

(b) from about 0.1 to about 1.0 grams of 1-phenyl-1,2- tetrazoline-S-thione or a tautomeric equivalent thereof;

(c) a buffering agent consisting essentially of from about 25 to about 150 grams of monobasic potassium phosphate.

2. A stabilizer solution of Claim 1 wherein said stabilizing agent comprises ammonium thiocyanate.

3. A stabilizer solution of Claim 2 wherein said ammonium thiocyanate is present in an amount of about 280:10 grams.

4. An aqueous photoprocessing stabilizer solution, comprising, per liter of solution:

Grams Ammonium thiocyanate 280110 Monobasic potassium phosphate 50:10 1-phenyl-1,2-tetrazoline-5-thione 05:2

5. In the processing of an exposed photosensitive silver halide emulsion including the steps of developing and stabilizing, the improvement comprising the use of an aqueous, acidic stabilizer composition containing, per liter of solution, from about 150 to about 350 grams of a watersoluble stabilizing agent selected from an alkali metal or ammonium thiocyanate, thiosulfate, thiourea, thioglycolic acid, or cominations of these, from about 0.1 to about 1.0 grams of 1-phenyl-1,2-tetrazoline-5-thi0ne or a tautomeric equivalent thereof, and a buffering agent consisting essentially of from about 25 to about 150 grams of monobasic potassium phosphate.

6. An improvement of Claim 5 wherein said stabilizing tagent comprises an alkali metal or ammonium thiocyana e.

7. An improvement of Claim 5 wherein said stabilizer composition comprises about 280: 10 grams of ammonium thiocyanate, 0520.2 grams of l-phenyl-1,2-tetrazoline-S-thione and 501-10 grams of monobasic potassium phosphate.

8. A process for developing an exposed photographic medium having a photosensitive silver halide emulsion thereon and having developing agents in the silver halide emulsion or in a layer contiguous thereto, comprising,

(a) contacting the medium with an alkaline activator solution for a period suflicient to develop a visible image; and

Grams Ammonium thiocyanate 280i 10 l-phenyl-1,2-tetrazoline-5-thione 0.5J -1.2 Monobasic potassium phosphate 50: 10

11. A process of Claim 10 wherein excess developing solution is removed from. said. photographic medium after development but prior to stabilization.

lieiarjn'cesjdi a I UNITED STATES PAT-ENTS' --:Willems-eta1:- F REIG P TENTS 1 MARY F. KELLEY, Primary Examiner.

Harris et a1. Nishio et a1.

" U.S. Cl. X.R. 

